1. Field of the Invention
The present invention relates to a discharge lamp lighting device which is capable of illuminating a capacitive discharge lamp.
2. Description of the Related Art
Conventionally, external electrode fluorescent lamps have been used as a reading light source for photocopiers, scanners, and the like. The external electrode fluorescent lamp has advantages in that it does not use mercury which may be detrimental to the environment. Further there is little change in the amount of light emitted by the external electrode fluorescent lamp with changes in the ambient temperature. The external electrode fluorescent lamp generates little heat, and the luminescent color thereof can be changed by selecting the fluorescent substance.
The illumination voltage waveform of an external electrode fluorescent lamp can be a sine waveform, for example. Other illumination voltage waveforms such as pulse waveform or rectangular waveforms have been used to improve luminous efficiency. Japanese Unexamined Patent Application Publication No. 2001-283783 describes an external electrode fluorescent lamp suitable for a document lighting light source.
An external electrode fluorescent lamp comprises electrodes located on the outside of the bulb, and connected to a capacity load which may comprise electrodes and/or the bulb. Also, an internal-external electrode discharge lamp may comprise electrodes on the inside and outside of the bulb. Further, an internal-internal electrode discharge lamp may comprise facing electrodes within the bulb, and a capacity load. Such lamps are illuminated by dielectric barrier discharge, and are called dielectric barrier discharge lamps.
With such a dielectric barrier discharge lamp, it is necessary to apply a high voltage at start-up time. However, in the event that a rectangular waveform or a pulse waveform is used for the lamp illumination voltage, sufficient illumination voltage may not be obtained, and the illumination starting time can fluctuate. Thus, it is difficult to obtain an appropriate illumination using these techniques.